The present invention relates to a micro electromechanical system (MEMS) microphone, a manufacturing method thereof, and an electronic device containing the same.
MEMS microphones are one of the most successful MEMS products, which are compatible with existing integrated circuits manufacturing techniques. MEMS microphones can be manufactured by using process techniques of semiconductor devices. Thanks to the continuous development of CMOS process technology, MEMS microphones can be made very small and have been used in a variety of wearable communication devices including mobile phones, tablet PCs, notebooks, still cameras, video cameras, hearing aids and others.
MEMS microphones can generally be capacitive microphones including a vibrating membrane (lower electrode) fixedly formed on a substrate and facing an opening disposed on a backside of the substrate, and a fixed plate (upper electrode) being suspended above the vibrating membrane. A sealed cavity is disposed between the vibrating membrane and the fixed plate. A MEMS microphone enables detection of a capacitive value change due to the displacement of the vibrating membrane in the sealed cavity, and the detected value change is then processed. However, a MEMS microphone is sensitive to signal interference so that a solution for reducing interference is required.
Current process techniques for manufacturing MEMS microphones employ deep reactive ion etching (DRIE) processes to etch the backside of a substrate to form an opening exposing the vibrating membrane. However, due to the large etched depth caused by deep reactive ion etching, the opening may have poor uniformity, thereby adversely affecting the acoustic signal quality of the microphone and degrading the microphone performance.
FIGS. 1A to 1D are cross-sectional views depicting stages of a conventional method of manufacturing a MEMS microphone according to the prior art.
Referring to FIG. 1A, a MEMS microphone includes a semiconductor substrate 100 having a front side and a backside, a sacrificial layer 101 disposed on the semiconductor substrate, a vibrating membrane 102 within the sacrificial layer, a fixed plate 103 disposed at a region corresponding to the vibrating membrane on the sacrificial layer, and a stopper structure 104 on the sacrificial plate. The stopper structure has multiple stopping elements disposed within sacrificial layer 101.
The MEMS microphone also includes a patterned photoresist layer 105 on the backside of the semiconductor substrate.
Referring to FIG. 1B, a deep reactive ion etching is performed onto the backside of semiconductor substrate 100 using patterned photoresist layer 105 as a mask until a surface of sacrificial layer 101 is exposed to form a cavity 106. Thereafter, patterned photoresist layer 105 is removed.
However, due to the large etch depth formed by the deep reactive ion etching process, cavity 106 may have a non-uniform (uneven) size in the range of about 15%. However, the MEMS microphone is very sensitive to the size variation of cavity 106. The poor uniformity of the cavity size will adversely affect the signal to noise ratio of the microphone, thereby degrading the microphone performance.
Referring to FIG. 1C, a portion of sacrificial layer 101 corresponding to cavity 106 is removed to release vibrating membrane 102, and concurrently form a second cavity 107 between vibrating membrane 102 and fixed plate 103.
Thereafter, the thus formed MEMS microphone is encapsulated in a case 120 (FIG. 1D). The displacement of the vibrating membrane 102 leads to a change in second cavity 107 that produces a signal difference, which is captured and processed by the MEMS microphone.
As described above, the prior art technique does not provide a smooth and uniform surface of the cavity when using a deep reactive ion etching process. The surface of the cavity tends to be uneven and the width of the cavity is non-uniform so that the sensitivity, signal to noise ratio and frequency response of the microphone are adversely affected.
Therefore, what is needed is a method for manufacturing a MEMS microphone that can provide a smooth and uniform cavity for an MEMS microphone.